1. Field of the Invention
The present invention relates to a picture signal processing system, and more particularly, to the improvement of a quantizer in a data compression (encoder) portion of the picture signal processing system.
2. Description of the Related Art
Generally, in an encoder portion of a picture signal processing system, a transform coding using an orthogonal transformation is carried out. For example, picture signals are divided into sub-blocks, and an orthogonal transformation such as a discrete cosine transformation (DCT) is performed upon each of the sub-blocks, to thereby obtain transformed coefficients. Then, in a quantizer, a quantization is performed upon the transformed coefficients, to thereby obtain quantization coefficients. Finally, the quantization coefficients are encoded and are transmitted to the exterior.
In a prior art quantizer, each of the transformed coefficients is divided by its corresponding quantization factor to a frequency component thereof. For this purpose, a divider is provided, to thereby complicate and increase the configuration of the quantizer. Also, the speed of operation of the quantizer is low. This will be explained later in more detail.
In another prior art quantizer, quantization factors are approximated to values denoted by 2.sup.k (k=1, 2, . . . ), and as a result, a single shifter is provided instead of the divider, thus simplifying and reducing the configuration of the quantizer. In this quantizer, the speed of operation is also increased (see: Japanese Patent Publication (Kokai) No. Hei 2-132972), which will explained later in more detail. In this prior art quantizer, however, when quantization factors are large, the interval therebetween is so large as to deteriorate the properties of a reproduced picture.